curs_getch(3X) Library calls curs_getch(3X)

getch, wgetch, mvgetch, mvwgetch, ungetch, has_key - get (or push back) characters from curses terminal keyboard

#include <curses.h>
int getch(void);
int wgetch(WINDOW *win);
int mvgetch(int y, int x);
int mvwgetch(WINDOW *win, int y, int x);
int ungetch(int c);
/* extension */
int has_key(int c);

wgetch gathers a key stroke from the terminal keyboard associated with a curses window win. ncurses(3X) describes the variants of this function.

When input is pending, wgetch returns an integer identifying the key stroke; for alphanumeric and punctuation keys, this value corresponds to the character encoding used by the terminal. Use of the control key as a modifier often results in a distinct code. The behavior of other keys depends on whether win is in keypad mode; see subsection “Keypad Mode” below.

If no input is pending, then if the no-delay flag is set in the window (see nodelay(3X)), the function returns ERR; otherwise, curses waits until the terminal has input. If cbreak(3X) has been called, this happens after one character is read. If nocbreak(3X) has been called, it occurs when the next newline is read. If halfdelay(3X) has been called, curses waits until a character is typed or the specified delay elapses.

If echo(3X) has been called, and the window is not a pad, curses writes the returned character c to the window (at the cursor position) per the following rules.

  • If c matches the terminal's erase character, the cursor moves leftward one position and the new position is erased as if wmove(3X) and then wdelch(3X) were called. When the window's keypad mode is enabled (see below), KEY_LEFT and KEY_BACKSPACE are handled the same way.
  • curses writes any other c to the window, as with wechochar(3X).
  • If the window has been moved or modified since the last call to wrefresh(3X), curses calls wrefresh.

If c is a carriage return and nl(3X) has been called, wgetch returns the character code for line feed instead.

To curses, key strokes not from the alphabetic section of the keyboard (those corresponding to the ECMA-6 character set—see ascii(7)—optionally modified by either the control or shift keys) are treated as function keys. (In curses, the term “function key” includes but is not limited to keycaps engraved with “F1”, “PF1”, and so on.) If the window is in keypad mode, these produce a numeric code corresponding to the KEY_ symbols listed in subsection “Predefined Key Codes” below; otherwise, they transmit a sequence of codes typically starting with the escape character, and which must be collected with multiple wgetch calls.

  • The curses.h header file declares many predefined function keys whose names begin with KEY_; these object-like macros have values outside the range of eight-bit character codes.
  • In ncurses, user-defined function keys are configured with define_key(3X); they have no names, but are also expected to have values outside the range of eight-bit codes.

A variable intended to hold a function key code must thus be of type short or larger.

Most terminals one encounters follow the ECMA-48 standard insofar as their function keys produce character sequences prefixed with the escape character ESC. This fact implies that curses cannot know whether the terminal has sent an ESC key stroke or the beginning of a function key's character sequence without waiting to see if, and how soon, further input arrives. When curses reads such an ambiguous character, it sets a timer. If the remainder of the sequence does not arrive within the designated time, wgetch returns the prefix character; otherwise, it returns the function key code corresponding to the unique sequence defined by the terminal. Consequently, a user of a curses application may experience a delay after pressing ESC while curses disambiguates the input; see section “EXTENSIONS” below. If the window is in “no time-out” mode, the timer does not expire; it is an infinite (or very large) value. See notimeout(3X). Because function key sequences usually begin with an escape character, the terminal may appear to hang in no time-out mode after the user has pressed ESC. Generally, further typing “awakens” curses.

ungetch places c into the input queue to be returned by the next call to wgetch. A single input queue serves all windows.

The header file curses.h defines the following function key codes.

  • Except for the special case of KEY_RESIZE, a window's keypad mode must be enabled for wgetch to read these codes from it.
  • Not all of these are necessarily supported on any particular terminal.
  • The naming convention may seem obscure, with some apparent misspellings (such as “RSUME” for “resume”); the names correspond to the terminfo capability names for the keys, and were standardized before the IBM PC/AT keyboard layout achieved a dominant position in industry.
Symbol Key name
KEY_BREAK Break key
KEY_DOWN Arrow keys
KEY_HOME Home key (upward+left arrow)
KEY_F0 Function keys; space for 64 keys is reserved
KEY_F(n) Function key n where 0 ≤ n ≤ 63
KEY_DL Delete line
KEY_IL Insert line
KEY_DC Delete character
KEY_IC Insert character/Enter insert mode
KEY_EIC Exit insert character mode
KEY_CLEAR Clear screen
KEY_EOS Clear to end of screen
KEY_EOL Clear to end of line
KEY_SF Scroll one line forward
KEY_SR Scroll one line backward (reverse)
KEY_NPAGE Next page/Page up
KEY_PPAGE Previous page/Page down
KEY_STAB Set tab
KEY_CTAB Clear tab
KEY_CATAB Clear all tabs
KEY_ENTER Enter/Send
KEY_SRESET Soft (partial) reset
KEY_RESET (Hard) reset
KEY_PRINT Print/Copy
KEY_LL Home down/Bottom (lower left)
KEY_A1 Upper left of keypad
KEY_A3 Upper right of keypad
KEY_B2 Center of keypad
KEY_C1 Lower left of keypad
KEY_C3 Lower right of keypad
KEY_BTAB Back tab key
KEY_BEG Beg(inning) key
KEY_CANCEL Cancel key
KEY_CLOSE Close key
KEY_COMMAND Cmd (command) key
KEY_COPY Copy key
KEY_CREATE Create key
KEY_END End key
KEY_EXIT Exit key
KEY_FIND Find key
KEY_HELP Help key
KEY_MARK Mark key
KEY_MESSAGE Message key
KEY_MOUSE Mouse event occurred
KEY_MOVE Move key
KEY_NEXT Next object key
KEY_OPEN Open key
KEY_OPTIONS Options key
KEY_PREVIOUS Previous object key
KEY_REDO Redo key
KEY_REFERENCE Ref(erence) key
KEY_REFRESH Refresh key
KEY_REPLACE Replace key
KEY_RESIZE Screen resized
KEY_RESTART Restart key
KEY_RESUME Resume key
KEY_SAVE Save key
KEY_SELECT Select key
KEY_SUSPEND Suspend key
KEY_UNDO Undo key
KEY_SBEG Shifted beginning key
KEY_SCANCEL Shifted cancel key
KEY_SCOMMAND Shifted command key
KEY_SCOPY Shifted copy key
KEY_SCREATE Shifted create key
KEY_SDC Shifted delete character key
KEY_SDL Shifted delete line key
KEY_SEND Shifted end key
KEY_SEOL Shifted clear line key
KEY_SEXIT Shifted exit key
KEY_SFIND Shifted find key
KEY_SHELP Shifted help key
KEY_SHOME Shifted home key
KEY_SIC Shifted insert key
KEY_SLEFT Shifted left arrow key
KEY_SMESSAGE Shifted message key
KEY_SMOVE Shifted move key
KEY_SNEXT Shifted next object key
KEY_SOPTIONS Shifted options key
KEY_SPREVIOUS Shifted previous object key
KEY_SPRINT Shifted print key
KEY_SREDO Shifted redo key
KEY_SREPLACE Shifted replace key
KEY_SRIGHT Shifted right arrow key
KEY_SRSUME Shifted resume key
KEY_SSAVE Shifted save key
KEY_SSUSPEND Shifted suspend key
KEY_SUNDO Shifted undo key

Many keyboards feature a nine-key directional pad.

A1 up A3
left B2 right
C1 down C3

Two of the symbols in the list above do not correspond to a physical key.

  • wgetch returns KEY_RESIZE, even if the window's keypad mode is disabled, when ncurses handles a SIGWINCH signal; see initscr(3X) and resizeterm(3X).
  • wgetch returns KEY_MOUSE to indicate that a mouse event is pending collection; see curs_mouse(3X). Receipt of this code requires a window's keypad mode to be enabled, because to interpret mouse input (as with with xterm(1)'s mouse prototocol), ncurses must read an escape sequence, as with a function key.

In ncurses, has_key returns a Boolean value indicating whether the terminal type recognizes its parameter as a key code value. See also define_key(3X) and key_defined(3X).

Except for has_key, these functions return OK on success and ERR on failure.

Functions taking a WINDOW pointer argument fail if the pointer is NULL.

Functions prefixed with “mv” first perform cursor movement and fail if the position (y, x) is outside the window boundaries.

wgetch also fails if

  • its timeout expires without any data arriving, or
  • execution was interrupted by a signal, in which case errno is set to EINTR.

ungetch fails if there is no more room in the input queue.

has_key returns TRUE or FALSE.

curses discourages assignment of the ESC key to a discrete function by the programmer because the library requires a delay while it awaits the potential remainder of a terminal escape sequence.

Some key strokes are indistinguishable from control characters; for example, KEY_ENTER may be the same as ^M, and KEY_BACKSPACE may be the same as ^H or ^?. Consult the terminal's terminfo entry to determine whether this is the case; see infocmp(1). Some curses implementations, including ncurses, honor the terminfo key definitions; others treat such control characters specially.

curses distinguishes the Enter keys in the alphabetic and numeric keypad sections of a keyboard because (most) terminals do. KEY_ENTER refers to the key on the numeric keypad and, like other function keys, and is reliably recognized only if the window's keypad mode is enabled.

  • The terminfo key_enter (kent) capability describes the character (sequence) sent by the Enter key of a terminal's numeric (or similar) keypad.
  • “Enter or send” is X/Open Curses's description of this key.

curses treats the Enter or Return key in the alphabetic section of the keyboard differently.

  • It usually produces a control code for carriage return (^M) or line feed (^J).
  • Depending on the terminal mode (raw, cbreak, or “cooked”), and whether nl(3X) or nonl(3X) has been called, wgetch may return either a carriage return or line feed upon an Enter or Return key stroke.

Use of wgetch with echo(3X) and neither cbreak(3X) nor raw(3X) is not well-defined.

Historically, the list of key code macros above was influenced by the function-key-rich keyboard of the AT&T 7300 (also known variously as the “3B1”, “Safari 4”, and “UNIX PC”), a 1985 machine. Today's computer keyboards are based that of the IBM PC/AT and tend to have fewer. A curses application can expect such a keyboard to transmit key codes KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT, KEY_HOME, KEY_END, KEY_PPAGE (Page Up), KEY_NPAGE (Page Down), KEY_IC (Insert), KEY_DC (Delete), and KEY_F(n) for 1 ≤ n ≤ 12.

getch, mvgetch, and mvwgetch may be implemented as macros.

In ncurses, when a window's “no time-out” mode is not set, the ESCDELAY variable configures the duration of the timer used to disambiguate a function key character sequence from a series of key strokes beginning with ESC typed by the user; see curs_variables(3X).

has_key was designed for ncurses(3X), and is not found in SVr4 curses, 4.4BSD curses, or any other previous curses implementation.

Applications employing ncurses extensions should condition their use on the visibility of the NCURSES_VERSION preprocessor macro.

X/Open Curses, Issue 4 describes getch, wgetch, mvgetch, mvwgetch, and ungetch. It specifies no error conditions for them.

wgetch reads only single-byte characters.

The echo behavior of these functions on input of KEY_ or backspace characters was not specified in the SVr4 documentation. This description is adapted from X/Open Curses.

The behavior of wgetch in the presence of signal handlers is unspecified in the SVr4 documentation and X/Open Curses. In historical curses implementations, it varied depending on whether the operating system's dispatch of a signal to a handler interrupting a read(2) call in progress, and also (in some implementations) whether an input timeout or non-blocking mode has been set. Programmers concerned about portability should be prepared for either of two cases: (a) signal receipt does not interrupt wgetch; or (b) signal receipt interrupts wgetch and causes it to return ERR with errno set to EINTR.

KEY_MOUSE is mentioned in X/Open Curses, along with a few related terminfo capabilities, but no higher-level functions use the feature. The implementation in ncurses is an extension.

KEY_RESIZE and has_key are extensions first implemented for ncurses. By 2022, PDCurses and NetBSD curses had added them along with KEY_MOUSE.

curs_get_wch(3X) describes comparable functions of the ncurses library in its wide-character configuration (ncursesw).

curses(3X), curs_addch(3X), curs_inopts(3X), curs_mouse(3X), curs_move(3X), curs_outopts(3X), curs_refresh(3X), curs_variables(3X), resizeterm(3X), ascii(7)

ECMA-6 “7-bit coded Character Set”

ECMA-48 “Control Functions for Coded Character Sets”

2024-04-20 ncurses 6.5